The invention is concerned with peroxide powder bleach compositions and their formation. More particularly, the invention relates to alkali metal percarbonate powder bleach compositions which exhibit a high degree of storage stability, and which can be produced to retain component proportions from the top to the bottom of the box filled therewith. Alkali metal percarbonate shall be the term used herein, although the alkali metal precarbonates are more properly believed to exist as the perhydrates of the alkali metal carbonates.